The present invention generally relates to metallization, patterning of electrodes onto block type filters, diplexers and resonators. The photo-definition method is especially useful on small resonators having any dimension less than 4 mm in size.
The concept of RF ceramic block type filters is well known in the art. Ceramic block filters are constructed of a high Q ceramic material and are typically coupled to other electronic circuitry through solder mounting pads, wires, cables and pins coupled to conductive connection points on external surfaces of the blocks. These ceramics are also used to construct duplexers and other electronic components. The production of block filters starts with a ceramic resonator, typically a square or rectangular part having a length, width and height, and in most cases this resonator will have a through hole in the center. The dimensions of the width and height are usually the same in a single resonator and these two dimensions define the profile of the block. Once the ceramic block is made, metallization (usually silver) is placed on all surfaces including the inside surface of the through hole. This is normally performed via a dip coating method. Typically, vendors of resonator products will then sand or blast off the metallization on the top surface only. Patterning of surfaces is usually not a provided service.
In prior art, a ceramic block is sintered and then blanket metallization is usually placed using a dip coating method. Then the sides that require metallization patterning are cleaned off or left uncoated. The patterning is traditionally performed by screen printing features directly on substrates followed by a firing step. However, in the present invention and devices of similar size, screen printing cannot be used due to the feature sizes and tolerances required. For example, the block part itself is a 3 mm times 3 mm square and in some cases the corners are rounded instead or square with a center through hole. The required spacing feature size was less than 4 mm with line sizes less than 10 mm. To ensure a good print with good edge definition and tolerances, this would be very expensive and nearly impossible. Also, due to the fact that the filter of the present invention is designed for 1.8-2.3 GHz range, the tolerances required are much more stringent than standard screen printing usually allows.
Another method in prior art for applying a pattern to a block ceramic filter is through a subtractive process such as chemical etching or laser ablation to take off the excess metal in order to obtain a pattern on the ceramic block. In the case of chemical etching of the metal, it is possible that the solutions used can adversely affect the ceramic material surrounding the pattern. Also because this step would be done post firing, the etching chemicals used are usually harsher than the method defined in this invention. For this process it would be difficult to produce a pattern on a rounded corner block.
Therefore, a strong need in the industry exists for a novel method to apply to metal etching.